Tilt-up buildings generally consist of those types of structures that are constructed with concrete wall panels that are precast horizontally on the ground, cured, and then tilted up into place.
The roof framing systems of older tilt-up and concrete block buildings that were built between the early 1950's (when the initial construction of tilt-up buildings began) and the mid 1960's were generally constructed with long-span timber roof trusses and timber roof joists. The timber trusses in these buildings were typically oriented to span the short direction of the building. Spacing between these trusses generally varies between 16 and 24 feet. The roof joists generally consist of 2×8's, 2×10's, 2×12's, or 2×14's spaced at 24″ o.c., and span between the timber trusses. At the perimeter of the building the roof joists span between the timber trusses and the tilt-up wall panels or concrete block walls, were they are typically framed onto a timber ledger that is bolted to the wall panel. Roof sheathing for these buildings typically consists of ⅜″ of ½″ plywood.
After the mid 1960's the roof framing systems of most tilt-up and concrete block buildings were generally constructed with glulam beams instead of long-span timber trusses and a “panelized” roof framing system instead of roof joists. These modifications to the roof framing systems of tilt-up and concrete block buildings were typically made for economic reasons.
A “panelized” roof framing system consists of timber purlins, timber sub-purlins (also known as stiffeners), and roof sheathing. The roof sheathing typically consists of 4′×8′ sheets of ⅜″ or ½″ thick plywood, and spans between the sub-purlins. These sub-purlins are generally 2×4's or 2×6's, and span between the purlins. The purlins typically consist of 4×12's or 4×14's and span between the glulam beams (or in some cases longspan timber trusses). The plywood sheathing is typically oriented with it's long dimension parallel to the sub-purlins, or perpendicular to the purlins. The sub-purlins are generally spaced 24″ apart. The purlins are typically spaced 8 feet apart to accommodate the length of the plywood sheathing. The glulam beams are typically spaced 20 to 24 feet apart. Sections of the panelized roof are typically fabricated on the ground and raised into place with a crane or forklift.
In areas subject to high seismicity, the connection between the concrete wall panels of most older tilt-up and concrete block buildings and their roof and floor framing systems is inadequate per the currently established seismic design standards for such buildings. Generally, this connection consists of only the nailing between the roof or floor sheathing and the timber ledger that is bolted to the wall panel or concrete block wall. This type of connection relies on a mechanism that subjects the ledgers to “cross grain bending”, a mechanism that is highly vulnerable to failure. The deficiencies associated with this type of connection were responsible for numerous failures and collapses of tilt-up and concrete block buildings during the 1971 San Fernando Earthquake. As a result, this type of connection has been specifically disallowed since the 1973 Edition of the Uniform Building Code.
In the 1976 Edition of the Uniform Building Code, the provisions disallowing wall tie connections that rely on timber elements subjected to cross grain bending were supplemented to also prohibit the use of load transfer mechanisms that subject timber elements to “cross grain tension”, a mechanism that is also highly vulnerable to failure. This provision effectively eliminated the use of plywood as a tension tie at the purlin and beam framing elements, and brought about the concept of sub-diaphragms and diaphragm continuity lines. This concept assumes that the forces associated with the wall tie system are transferred into a sub-diaphragm, a smaller portion of the overall roof (or floor) diaphragm that consists of the roof (or floor) framing elements and the associated plywood sheathing. The sub-diaphragm is intended to provide for the transfer of these loads to the diaphragm continuity lines, which extend across the buildings overall roof (or floor) diaphragm. The continuity lines are intended to transfer loads into the overall roof (or floor) diaphragm, which are then transferred to diaphragm collector elements and/or lateral load resisting elements, such as shear walls and/or steel frames. Diaphragm continuity lines are generally formed by interconnecting the major roof (or floor) framing elements together with continuity ties.
In general, most tilt-up and concrete block buildings are now constructed with discrete wall and diaphragm continuity ties. For existing tilt-up and concrete block buildings that were constructed without discrete wall and continuity ties, it is generally recommended that they be retrofitted with new connections per the currently established seismic design standards and/or recommendations for such buildings.
Wall and continuity tie installations typically consist of a connection bracket that is attached to either one or both sides of a roof (or floor) framing element, and attached to the wall in a wall tie installation, or another roof (or floor) framing element (with similar connection brackets attached) with a rod element in a continuity tie installation. At the present time the bolted connection devices that are most commonly used for wall and continuity tie applications are referred to as holdowns and continuity ties. An example of a holdown connection bracket is disclosed in U.S. Pat. No. 5,249,404. An example of a continuity tie connection bracket is disclosed in U.S. Pat. No. 5,813,181. The problems and deficiencies associated with the use of holdowns in wall and continuity tie applications are very significant, and are disclosed in U.S. Pat. No. 5,813,181.
Current continuity tie brackets generally consist of a rectangular box that defines the body element of the device. The body element is formed by bending a single piece of metal into the rectangular shape. End bearing plates are welded to both ends of the body element. A hole is provided in each end bearing plate, which allows for a rod element to extend through the body element of the continuity tie bracket. The rod hole can be located at the center of the end bearing plate, or offset in order to provide clearance between the rod and any potential interfering items associated with a wall or continuity tie installation, such as a metal support hanger at the end of a purlin in a panelized roof framing system. Nuts are used to secure the rod element to end bearing plates of the continuity tie bracket, allowing for the rod to transfer loads bi-directionally, in tension and compression. In order to secure the continuity tie bracket to the building structural member, a series of holes are provided through two of the opposing walls of the body element. This allows for installation of bolts that extend through these holes, and the body element, and into the roof (or floor) framing element of the building. The bolt holes in a continuity tie bracket are typically arranged in a staggered sequence on either side of the rod element in order to maximize the distance between the bolts.
A problem associated with the rectangular continuity tie bracket is that the bracket is heavy. The bracket is typically fabricated from steel in order to provide sufficient load capacity for the applications for which it is intended at reasonably economic costs. The sub-elements of the bracket are generally fabricated from materials of constant thickness. The thickness of these sub-components is usually predicated on the load capacity required at one critical location, and thus may be unnecessarily thick at all other locations. The result of this situation is a rectangular continuity tie bracket that can be unnecessarily heavy and awkward to handle during installation. As will be recognized by those of ordinary skill in the art, the continuity tie brackets are typically installed in roof and floor framing systems where access is only obtainable with lifts or ladders. Fatigue of the installer is a concern when working on ladders. Therefore, the weight of the continuity tie bracket is a concern in order to reduce fatigue of the installer during the installation process.
Furthermore, it is difficult to consistently manufacture the rectangular continuity tie brackets. As previously mentioned above, the rod holes can be offset from the center of the end bearing plates and formed before the end bearing plate is welded to the body element. It is possible during the manufacturing process to install the end bearing plates incorrectly, such that the offset rod holes do not align and the rod cannot extend through the bracket.
Another drawback of the current continuity tie bracket is that in situations where brackets with offset rod holes are used in paired installations, with one bracket installed on each side of a structural framing element, a matched set of brackets must be used in order for the bolt holes in one bracket to align with the bolt holes of the other bracket. Specifically, the bolts used to attach the brackets to the beam must extend through both of the brackets. Therefore, the bolt holes must align between the two brackets in order to attach the brackets to the structural framing element.
The present invention addresses the above-mentioned deficiencies in the prior art continuity tie bracket by providing a geometry that facilitates ease of installation. Furthermore, the geometry of the bracket facilitates consistent manufacturing without errors. Additionally, the present invention can be configured so that there is no need for matched brackets for paired installations.